In an electrophotographic image forming apparatus such as an electrostatic copying machine, a laser printer, a plain paper facsimile machine or a copier-printer-facsimile multifunction machine, a driving roller is employed for rotatively driving a sheet feed belt, a transfer belt, an intermediate transfer belt or the like.
The conventional driving roller is roughly classified into a crosslinked rubber type or a coating type.
For the driving roller of the former crosslinked rubber type, a crosslinkable rubber such as an EPDM is used as a base polymer, and a crosslinkable rubber composition is prepared by blending a plasticizer, a filler, a crosslinking agent, an electrically conductivity imparting agent and the like with the base polymer, and kneading the resulting mixture. Then, the driving roller is produced by extruding the crosslinkable rubber composition into a roller body and crosslinking the roller body.
The driving roller of the latter coating type is produced as having a thin coating layer having a thickness of not greater than about 0.3 mm by applying a coating agent containing a curable binder resin such as a urethane resin on an outer peripheral surface of a metal roller, and curing the binder resin.
The type of the driving roller to be selected is dependent upon required characteristic properties. The production of the driving roller of the former crosslinked rubber type problematically requires higher production costs with lower productivity, because the rubber kneading step and the crosslinking step are performed on a batch basis.
The production of the driving roller of the latter coating type also problematically requires higher production costs with lower productivity, because it is difficult to properly control the quality of the coating agent or to uniformly apply the coating agent on the outer peripheral surface of the roller. Further, the thin coating layer is liable to be worn out in a short period of time.
It is contemplated to use a thermoplastic elastomer composition containing a thermoplastic elastomer as a base polymer instead of the crosslinkable rubber composition for production of a sheet feed roller, a charging roller and a transfer roller to be incorporated, like the driving roller, in the image forming apparatus (see PTL1 and PTL2).
For the sheet feed roller and the like to be produced from the thermoplastic elastomer composition, for example, the thermoplastic elastomer composition is continuously prepared with the use of an extruder. Without the need for the batch-based rubber kneading step and the batch-based crosslinking step subsequent to the extruding step, the production of these rollers can be achieved with improved productivity at lower costs. Where the driving roller is produced from the thermoplastic elastomer composition in the same manner as the sheet feed roller and the like, therefore, it is expected to provide the same effects.